This invention relates generally to electrical power supplies, and more particularly to a power supply system for feeding a plurality of loads such for example as electric-discharge lamps or gas-discharge lamps, featuring provisions for automatically balancing the currents fed to such loads.
Gas-discharge lamps such as cold-cathode fluorescent lamps (CCFLs) find extensive use for liquid crystal display (LCD) backlighting and other applications. Such lamps are lit up by an igniter incorporating a high frequency inverter, as disclosed in Japanese Unexamined Patent Publication No. 5-242987.
Built to the same stringent manufacturing specifications, the individual gas-discharge lamps might nevertheless differ in impedance and so incur an unequal flow of current therethrough. The result, in the case of LCD backlights, would be uneven display screen brightness. Japanese Unexamined Patent Publication No. 11-238589 represents a conventional remedy (shown in FIG. 1 of the drawings attached hereto) for this problem. It teaches a gas-discharge lamp igniter wherein each two lamps are connected between the pair of output terminals of an AC power supply via a pair of windings, respectively of one current-balancing transformer. Each pair of current-balancing transformer windings are interconnected, and each two pairs of current-balancing transformer windings are connected to one of the pair of output terminals of the AC power supply via an additional pair of current-balancing transformer windings, respectively. In short the lamps are energized under cascade control of the current-balancing transformers. Each pair of current-balancing transformer windings are oppositely polarized.
All such current-balancing transformers used in the gas-discharge lamp igniter are not free from some inherent fluctuations in performance. These performance fluctuations, be they ever so slight in individual transformers, become aggravated as the balancing of the lamp energization is sought to be attained by cascade connection of current-balancing transformers as in the prior art cited above. It has indeed sometimes occurred for the gas-discharge lamps to glow with unequal intensity for this reason.